constraints,template specialization,drop IFTI

[Max Samukha]

On Wed, 15 Jul 2009 20:00:40 +0200, BLS <windevguy at hotmail.de> wrote:

>Jarrett Billingsley wrote:
>> On Wed, Jul 15, 2009 at 1:42 PM, BLS<windevguy at hotmail.de> wrote:
>>> Quote : "
>>> Constraints are not involved with determining which template is more
>>> specialized than another. "
>> 
>> Well that is *completely* lame.  I would have expected
>> 
>> template Foo(int N : 5)
>> 
>> to be sugar for
>> 
>> template Foo(int N) if(N == 5)
>> 
>> Why *isn't* that the case?
>
>Tu me demande ? Pas d' idee. ..have to ask the gurus

And template oveloading with refined concepts is not supported, which
makes constraints less useful than C++'s concepts:

// InputRange concept
template isInputRange(T)
{
....
}

// Refinement of InputRange concept
template isForwardRange(T)
{
    enum isForwardRange = isInputRange!T && ....;
}

void foo(T)(T r) if (isInputRange!T)
{
}

void foo(T)(T r) if (isForwardRange!T)
{
}

void bar()
{
    ForwardRange fr;
    InputRange ir;
    foo(fr); 
    foo(ir);
}

The above doesn't compile, of course. The limitation can be worked
around in a number of graceless ways but claiming that D's constraints
are superior to C++ concepts seems to be premature.